#include <iostream>
using namespace std;

int binarySearch(int a[],int key,int n)
{
	int left=0;
	int right=n-1;
	while(left<=right){
		int middle=(left+right)/2;
		if(key==a[middle]) return middle;
		else if(key>a[middle]) left=middle+1;
		else right=middle-1;
	}
	return -1;
} 


int main()
{
	int a[100];
	int n;
	cin>>n;
	for(int i=0;i<n;i++) cin>>a[i];
	cout<<binarySearch(a,10,n);
	return 0;
}
